Fix incomplete teardown of demuxer.

I ran into an issue with PipelineIntegrationTests where one of the
security videos was causing ~FileDataSource to DCHECK complain about
file_ never being torn down.

Tracing this back, it's because we return NULL for the demuxer when
an error is encountered. This prevents demuxer->Stop() from being called
which leaves the data source in an unhappy state.

BUG=none
TEST=PipelineIntegrationTests/media_unittests


Review URL: http://codereview.chromium.org/9350004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@120730 0039d316-1c4b-4281-b951-d872f2087c98

media/base/pipeline.cc

@@ -1139,17 +1139,13 @@ void Pipeline::OnDemuxerBuilt(PipelineStatus status, Demuxer* demuxer) {
     return;
   }
 
+  demuxer_ = demuxer;
   if (status != PIPELINE_OK) {
     SetError(status);
     return;
   }
 
-  if (!demuxer) {
-    SetError(PIPELINE_ERROR_REQUIRED_FILTER_MISSING);
-    return;
-  }
-
-  demuxer_ = demuxer;
+  CHECK(demuxer_) << "Null demuxer encountered despite PIPELINE_OK.";
   demuxer_->set_host(this);
 
   {

media/filters/ffmpeg_demuxer_factory.cc

@@ -22,11 +22,7 @@ FFmpegDemuxerFactory::~FFmpegDemuxerFactory() {}
 static void DemuxerInitDone(const DemuxerFactory::BuildCallback& cb,
                             const scoped_refptr<FFmpegDemuxer>& demuxer,
                             PipelineStatus status) {
-  if (status != PIPELINE_OK) {
-    cb.Run(status, NULL);
-    return;
-  }
-  cb.Run(PIPELINE_OK, demuxer);
+  cb.Run(status, demuxer);
 }
 
 void FFmpegDemuxerFactory::Build(const std::string& url,